3D printing or additive manufacturing (AM) is a process for manufacturing a 3D object of any shape from a 3D model or other electronic databases through additive processes in which successive layers of material are placed under computer controls.

Nowadays, rapid prototyping has a huge range of applications in several fields of human activity: research, engineering, military, construction, medical industry, architecture, the computer industry, fashion, education, and many others.

Principles of 3D Printing

1. Modeling

3D modeling is a process of analyzing and collecting data on appearance and the shape of an object. Based on this data, 3D models of the scanned objects are manufactured.

Both manual and automatic creations of these models are very tough for consumers. 3D printable models can be created via CAD design packages or via 3D scanner.

2. Printing

Prior to printing a 3D model from. STL file, it must be administered by a software called a “slicer” that alters the 3D model into a series of thin layers and generates a G-code file from.

STL file having instructions to a printer. There are many open source slicer programs. The layers correspond to the actual cross-section. They are laid and fused together to form a 3D printed model.

The printer-produced resolution is enough for a wide range of applications, but printing to some extent an oversized version of the object in standard resolution and then getting rid of material with a higher-resolution process can attain greater precision.

Methods for 3D Printing

1. Selective Deposition Lamination

It is a main 3D printing process. There is an impulse to compare this process with the Laminated Object Manufacturing (LOM) process due to similarities in layering and shaping paper to form the final part. However, that is where similarity comes to an end.

The SDL 3D printing process constructs parts layer by layer using standard copier paper. Each new layer is fixed to the existing layer using an adhesive, which is applied selectively according to the 3D data provided to the machine.

This means that a much higher density of adhesive is settled down in the area that will become the part, and a much lower density of adhesive is applied in the environmental area that will serve as the support, making sure relatively easy “weeding,” or support removal.

After a new sheet of paper is put into the 3D printer from the paper feed mechanism and rested on top of the selectively applied adhesive on the existing layer, the build plate is moved up to a heat plate and pressure is applied. This pressure makes sure a positive bond between the two sheets of paper.

The build plate then returns to the building height where an adjustable tungsten carbide blade cuts one sheet of paper at a time, tracing the object outline to create the edges of the part. When this cutting off is finished, the 3D printer accumulates the next layer of adhesive and so on until the part is complete.

It is largely identified as the first 3D printing process; it was the first to be materialistic. SL is a laser-based method that works with photo-polymer resins, that react with the laser and crosslink to form a solid.

It is a complex process but simply put, the photopolymer resin is held in a vat with a transportable platform inside. A laser beam is directed in the X-Y axis over the surface of the resin according to the 3D data provided to the machine, whereby the resin hardens exactly where the laser hits the surface.

Once the layer is finished, the platform within the vat drops down by a fraction (in the Z-axis) and the following layer is detected out by the laser. This continues until the entire object is completed and the platform can be lifted out of the vat for taking out.

Because of the nature of this method, it requires support formations for some parts, mainly those which are bulged out. These structures need to be manually separated. Many objects 3D printed using this method need to be cleaned and cured. Curing involves subjecting the part to severe light in an oven-like machine to fully cure the resin.

Stereolithography is generally adopted as being one of the most precise 3D printing processes include the post-processing steps required with the good surface finish. However, disadvantages and the stability of the materials over time, which can become more fragile.

3. DLP (Digital Light Processing)

It is a similar process to SL. The major difference is the light source. DLP uses a more conventional light source, such as an arc lamp, with a liquid crystal display panel or a deformable mirror device (DMD), which is applied over an entire surface of the vat of photopolymer resin in a single run, making it faster than SL.

Like SL, DLP builds highly precise parts with excellent resolution, but its sameness also includes the same needs for support structures and post-crosslinking. However, one superiority of DLP over SL is that only a shallow vat of resin is required to ease the process, which generally results in less waste and lower running value.

4. Laser Sintering And Laser Melting

These are exchangeable terms that introduce a laser-based 3D printing method that works with powdered materials. The laser is detected over a powder bed of firmly compressed powdered material, according to the 3D data put to the machine, in the X-Y axis.

As the laser interferes with the surface of the powdered material it fuses, the particles to each other forming a solid. As each layer is over the powder bed drops additionally and a roller levels the powder over the surface of the bed initial to the next pass of the laser for the following layer to be created and sintered with the foregoing layer.

The build chamber is completely isolated as it is necessary to maintain accurate temperature during the method particular to the melting point of the powdered material of possibility. When finished, the whole powder bed is removed from the machine and the surplus powder can be removed to quit the ‘printed’ parts.

Advantages of this method are that the powder bed provides as an in-process support structure for bulged outs, and hence compound shapes that could not be produced in any other way are possible with this method. However, the disadvantage, because of the high temperatures required for laser sintering, cooling times can be appreciable.

In addition, porosity has been a historical difficulty with this method, and while there have been noteworthy advancements towards fully thick parts, some applications still necessitate infiltration with another material to upgrade mechanical features.

Laser sintering can method plastic and metal materials, even if metal sintering does need a much higher-powered laser and higher in-process conditions. Parts produced with this method are much well-built than with SL or DLP.

5. Electron Beam Melting

This method is very similar to the Direct Metal Laser Sintering (DMLS) process in terms of the generation of parts from metal powder. The main dissimilarity is the heat source, which, is an electron beam, rather than a laser, which necessitates that the method is brought out under vacuum surroundings.

It has the ability to construct fully- dense parts in a diversity of metal alloys, even to the medical category, and as an outcome, the process has been specifically victorious for a range of production applications in the medical industry, especially for implants. Although, other hi-tech sections such as aerospace and automotive have also looked to EBM technology for processing fulfillment.

6. Inkjet Binder Jetting

The material being jetted is a binder and is sprayed into a powder bed of the part material to blend it a layer at a time to print the essential part. With other powder bed systems, once a layer is completed, the powder bed drops additionally and a roller smoothens the powder across the surface of the bed, initial to the next pass of the jet heads, with the binder for the following layer to be formed and blended with the following layer.

Advantages of this, like with SLS, incorporate the fact that the need for supports is nullified because the powder bed itself supplies this functionality. However, a range of different materials can be used, counting ceramics and food.

A further typical advantage of the method is the ability to simply add a full-color palette which can be added to the binder. The parts resulting directly from the machine, moreover, are not as tough as with the sintering method and needs post-processing to ensure durability.

7. Inkjet Material Jetting

3D printing process by which the actual build materials (in liquid or molten state) are selectively jetted through many jet heads. Furthermore, the materials tend to be liquid photopolymers, which are cross-linked with a pass of UV light as each layer is settled.

The nature of product permits for the continuous settling of a range of materials, which means that a single part can be made from many materials with different functions and properties. Material jetting is a very accurate method, giving precise parts with a very flat finish.

8. Extrusion/FDM/FFF

Extrusion of thermoplastic material is most common for this method. The most common name for the method is fusion deposition modeling (FDM), due to longevity. The process works by melting plastic strand that is placed, via a heated extruder, a layer at a time, onto a build platform according to the 3D data provided to the printer.

Each layer crosslinks as it is placed and bonds to the foregoing layer. The FDM/FFF processes require support structures for any applications with bulging geometries. For FDM, this requires a second, water-soluble material, which permits support structures to be relatively washed, once the print is complete.

Alternatively, splinter support materials are also possible, which can be removed by manually separating them off the part. Support structures, or lack thereof, have generally been a disadvantage of the entry level FFF 3D printers. Furthermore, as the systems have engaged and developed to include dual extrusion heads, it has become less of a matter.

The process can be time-consuming for some segment of geometries and layer-to-layer adhesion can be an issue, resulting in segments that are not watertight. Post-processing using acetone can resolve these problems.

Conclusion

3D printing was first invented in the 1980’s and since then there has been a tremendous development in this technology. This is very much evident from the range of printing processes that are available today.

Right from metals, ceramics, thermoplastics to composites majority of the materials can be printed using 3D printing. 3D printing has benefitted various field but one field that has benefitted tremendously is medicine.

A lot of research is going on into personalized medicines and 3D printing is useful because of its fast production rates, low waste generation, and patient-specific production.

At the moment, large-scale industrial production is not been done but in the coming years, 3D printing will surely help in revolutionizing the manufacturing process.